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Inhibition of the transcriptional repressor complex Bcl-6/BCoR induces endothelial sprouting but does not promote tumor growth.

ABSTRACT: The oncogenic potential of the transcriptional repressor Bcl-6 (B-cell lymphoma 6) was originally discovered in non-Hodgkin patients and the soluble Bcl-6 inhibitor 79-6 was developed to treat diffuse large B-cell lymphomas with aberrant Bcl-6 expression. Since we found Bcl-6 and its co-repressor BCoR (Bcl-6 interacting co-repressor) to be regulated in human microvascular endothelium by colorectal cancer cells, we investigated their function in sprouting angiogenesis which is central to tumor growth. Based on Bcl-6/BCoR gene silencing we found that the transcriptional repressor complex in fact constitutes an endogenous inhibitor of vascular sprouting by supporting the stalk cell phenotype: control of Notch target genes (HES1, HEY1, DLL4) and cell cycle regulators (cyclin A and B1). Thus, when endothelial cells were transiently transfected with Bcl-6 and/or BCoR siRNA, vascular sprouting was prominently induced. Comparably, when the soluble Bcl-6 inhibitor 79-6 was applied in the mouse retina model of physiological angiogenesis, endothelial sprouting and branching were significantly enhanced. To address the question whether clinical treatment with 79-6 might therefore have detrimental therapeutic effects by promoting tumor angiogenesis, mouse xenograft models of colorectal cancer and diffuse large B-cell lymphoma were tested. Despite a tendency to increased tumor vessel density, 79-6 therapy did not enhance tumor expansion. In contrast, growth of colorectal carcinomas was significantly reduced which is likely due to a combined 79-6 effect on cancer cells and tumor stroma. These findings may provide valuable information regarding the future clinical development of Bcl-6 inhibitors.

SUBMITTER: Buchberger E

PROVIDER: S-EPMC5352177 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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Inhibition of the transcriptional repressor complex Bcl-6/BCoR induces endothelial sprouting but does not promote tumor growth.

Buchberger Elisabeth E Payrhuber Dietmar D El Harchi Miriam M Zagrapan Branislav B Scheuba Katharina K Zommer Anna A Bugyik Edina E Dome Balazs B Kral Julia Barbara JB Schrottmaier Waltraud Cornelia WC Schabbauer Gernot G Petzelbauer Peter P Gröger Marion M Bilban Martin M Brostjan Christine C

Oncotarget 20170101 1

The oncogenic potential of the transcriptional repressor Bcl-6 (B-cell lymphoma 6) was originally discovered in non-Hodgkin patients and the soluble Bcl-6 inhibitor 79-6 was developed to treat diffuse large B-cell lymphomas with aberrant Bcl-6 expression. Since we found Bcl-6 and its co-repressor BCoR (Bcl-6 interacting co-repressor) to be regulated in human microvascular endothelium by colorectal cancer cells, we investigated their function in sprouting angiogenesis which is central to tumor gr ...[more]

PMID: 27880939

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Project description:Branching from conduits is a defining feature of the gas delivery systems of invertebrates (tracheae built from epithelial cells) and vertebrates (vasculature lined by endothelial cells). Here, we show that the vertebrate transcriptional repressor Tel plays an evolutionarily conserved role in angiogenesis: it is indispensable for sprouting of primary human endothelial cells and for the normal development of the Danio rerio embryo blood circulatory system. Tel controls endothelial sprouting via binding to the generic co-repressor C-terminal binding protein (CtBP). In endothelial cells, the Tel:CtBP complex temporally restricts a VEGF-mediated pulse of dll4 expression and consequently integrates VEGFR intracellular signaling and intercellular Notch-Dll4 signaling. It further refines branching by regulating expression of other factors that constrain angiogenesis such as sprouty family members and ve-cadherin. Thus, the Tel:CtBP complex moderates the balance between positive and antagonistic angiogenesis cues and thereby conditions endothelial cells for angiogenesis. Since the activity of CtBP is attuned to intracellular NADH levels, our results raise the possibility that Tel-mediated sprouting could be sensitized to the metabolic status of the tissue. Tel control of branching appears to be evolutionarily conserved since Yan, the invertebrate orthologue of Tel, is similarly required for branching morphogenesis of the invertebrate tracheae. Collectively, our work suggests that Tel is a central regulator of angiogenesis and highlights Tel and its associated networks as potential targets for the development of therapeutic strategies to inhibit pathological angiogenesis. 2 independent screens were performed testing effects of knockdown of Tel or CtBP (screen 1) or effects of VEGF-A (screen 2) on Human Umbilical Vein Endothelial Cells (HUVECs). For screen 1 we tested 3 different conditions. We established stable HUVEC cell lines which were either infected with control lentivirus (Mock), or lentivirus expressing short hairpin RNA constructs for the specific knockdown of Tel(Teli) or CtBP2 (CtBP2i). Expression in the Teli and CtBP2i cell lines was compared to expression in the Mock cell line for screen 1. For screen 2 we tested 2 conditions. We exposed HUVECs to VEGF (50ng/mL) for 30 minutes (samplename: VEGF30) and compared the transcriptome of these cells to untreated HUVECs (VEGF0). For each condition 2 independent repeats were analyzed and expression of genes was averaged for each repeat. HUVECs were grown under standard conditions (37degrees Celsius, 5% CO2) in EGM2 medium (Lonza).

Dataset Information

Inhibition of the transcriptional repressor complex Bcl-6/BCoR induces endothelial sprouting but does not promote tumor growth.

Publications

Inhibition of the transcriptional repressor complex Bcl-6/BCoR induces endothelial sprouting but does not promote tumor growth.

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